Employee Benefit Plans - Amounts Included in Regulatory Asset and Accumulated Other Comprehensive Income/Loss Recognized as Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	$ (14)			$ (45)
Net loss	172			517
Recognized from accumulated other comprehensive loss	92	[1]		275	[1]
Recognized from regulatory asset	66			197
Total recognized in net periodic benefit cost	158			472
Chesapeake Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	0		(1)	(1)		(4)
Net loss	57		85	171		255
Recognized from accumulated other comprehensive loss	57	[1]		170	[1]
Total recognized in net periodic benefit cost	57			170
FPU Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss	81		43	243		131
Recognized from accumulated other comprehensive loss	15	[1]		46	[1]
Recognized from regulatory asset	66			197
Total recognized in net periodic benefit cost	81			243
Chesapeake Pension SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	5		5	14		15
Net loss	16		11	48		34
Recognized from accumulated other comprehensive loss	21	[1]		62	[1]
Total recognized in net periodic benefit cost	21			62
Chesapeake Postretirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	(19)		(20)	(58)		(60)
Net loss	18		18	55		53
Recognized from accumulated other comprehensive loss	(1)	[1]		(3)	[1]
Total recognized in net periodic benefit cost	$ (1)			$ (3)

[1] See Note 8, “Accumulated Other Comprehensive Income (Loss).